In general, according to a drum type washing method, detergent, washing water and the laundry are introduced and washing is performed by using a friction power between a rotating drum and the laundry after receiving a drive force of a motor. Thereby, the drum type washing method has not only an enhanced washing efficiency but also little laundry damage and laundry tangle.
According to a driving method of a motor thereof, a conventional drum type washing machine is classified into an indirect drive type in which driving force of a motor is indirectly transmitted to a drum through a belt tied around a motor pulley and a drum pulley, and a direct drive type in which driving force of a motor is directly transmitted to a drum by reason that a rotor of a BLDC motor is directly connected to a drum.
However, the indirect method has some problems of energy loss and a lot of noise, which are caused in a process transmitting the driving force.
Demands for direct drive type drum-type washing machine using a BLDC motor have been increasing accordingly so as to solve the above problems.
Referring to FIG. 1, a related art drum type washing machine will be described.
As shown in FIG. 1, a tub 2 is mounted within a cabinet 1, and a drum 3 is rotatably mounted in a center of the tub 2.
A motor having a stator 6 and a rotor 5 is mounted in rear of the tub 2. The stator 6 is secured on a rear wall of the tub, and the rotor 5 passes through the tub and is connected to the drum 3 by a shaft with covering the stator 6. Magnets are alternatively provided on an inner circumferential surface of the rotor 5 in opposite poles.
A tub supporter made of metal (not shown) which has almost the same appearance of an exterior of the rear wall of the tub 2 is interposed between the rear wall of the tub and the stator for maintaining concentricity of the stator as well as supporting load of the stator by being secured to the rear wall of the tub.
On the other hand, a door 7 is provided in front of the cabinet 1, and a gasket 8 is provided between the door 7 and the tub 2.
Also, a suspension spring 9a is provided between an inner surface of the cabinet's upper portion and an outer circumferential surface of the tub's upper portion for supporting the tub 2. A friction damper 9b is provided between an inner surface of the cabinet's lower portion and an outer circumferential surface of the tub's lower portion for dampening vibration of the tub 2 generated in a spinning cycle.
FIG. 2 is an enlarged sectional view of the motor. The stator 6 is secured to a bearing housing 2a on a rear surface of the tub 2, and the rotor 5 is rotoatably mounted in an outer of the stator 6. A first end of a shaft 4 is secured to a center of the rotor 5, and a second thereof is secured to a rear surface of the drum 3. A permanent magnet 5a is mounted on the inner circumferential surface of the rotor 5, and the stator 6 is employed as an electromagnet due to a core and a coil wound on an outer circumferential surface of the core.
Hence, once power is supplied to the coil, the rotor 5 rotates due to rotating magnetic field created between the permanent magnet and the electromagnet, and rotation torque of the rotor 5 is transmitted to the drum 3 through the shaft 4.
However, the above related art motor has a limitation of increasing output and power, because it uses one rotor.
In other words, output torque and power of a motor should be increased to rotate a drum of a washing machine as capacity thereof is enlarged. Hence, the size of the rotor and stator is also enlarged so as to increase the output of the motor. Thereby, it may cause a problem that size and weight of a motor should be increased.